The subject matter disclosed herein relates generally to gradient and more particularly to a gradient coil capable of generating multiple Fields-of-View (FOVs) in an imaging system.
Magnetic Resonance Imaging (MRI) systems typically include a superconducting magnet that generates a primary magnetic field within an imaging volume. The MRI system may also include gradient coils to generate a gradient field about a bore of the magnet. Generally, a patient is positioned on an examination table and inserted into the bore of the magnet. The magnet generates a uniform magnetic field B0 throughout the bore. The gradient coils extend around the bore and are energized to impose time and spatially varying magnetic fields on the uniform magnetic field.
In, general the larger FOV lowers the performance rating for that respective gradient coil. That is a gradient coil with a larger FOV requires more power to produce a given gradient strength than a gradient coil having a smaller FOV. Because coil inductance increases with the FOV size, the slew rate, i.e. the maximum rate of change of magnetic field gradient that can be generated by a gradient coil with a large FOV is reduced for a given power supply. Additionally, since gradient coils with larger FOVs typically expose the patient to a higher rate of change of magnetic field (dB/dt) that may result in peripheral nerve stimulation, imaging protocols utilizing higher gradient power and higher slew rates are generally performed on MRI systems equipped with a small FOV gradient set. Accordingly, it is desirable to optimize the FOV for a specific imaging procedure.
To optimize the FOV for a specific imaging procedure, at least one known MRI system includes at least one gradient coil and a different higher order gradient coil that is mounted separately from the gradient coil. Typically, the higher order gradient coil is mounted radially outwardly from the primary gradient coil such that the higher order gradient coil is radially separated from the gradient coil by a distance or gap. During operation, the magnetic field of the higher order gradient coil is varied to increase or decrease the size of the FOV. However, manufacturing an imaging system that includes two separate gradient coils that are installed at two different radial locations increases the complexity of the imaging system, which may also result in increased costs to manufacture the imaging system.